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DURABILITY AND PERFORMANCE
OF TITANIUM DIOXIDE IN
PHOTOCATALYTIC
PAVEMENTS Marwa Hassan Performance Contractors Distinguished Assistant Professor
Department of Construction Management
3128 Patrick Taylor Hall
Louisiana State University
Baton Rouge, LA 70803
Tel: (225) 578-9189
Introduction
The US faces a significant challenge in controlling
air pollution from transportation activities
Road microenvironments contribute:
29% of the volatile organic compounds
35% of the nitrogen oxides (NOx)
58% of the carbon monoxide
Tall buildings prevent the dispersion of air
pollutants in urban areas
Introduction
35 million Americans live within 300ft from roads
Decomposition of pollutants by ultraviolet (UV)
radiation is extremely slow
2008 Non-Attainment Areas (EPA)
Photocatalytic Mechanism
Titanium dioxide forms highly oxidizing holes and
photo-generated electrons resulting in powerful
oxidizing and reductive agents hydroxyl radicals and
superoxides.
Conduction
Band
Valence Band
Light (hv) Eg =3.2 eV
H2O
TiO2
e-
h+ Hydroxyl radical
(·OH)
Superoxides
(O2-)
NOx Photodegradation
NOx Degradation:
Sulfur dioxide is decomposed to sulfate
Hydrophobic or hydrophilic properties of the
surface allow them to self-clean in the presence of
rain
Photodegradation Efficiency
TiO2 crystal (anatase, brookite, rutile)
Substrate
Application method
Concentration of TiO2
Type and Concentration of Pollutants
Flow Rate
Relative Humidity
Interaction between multiple pollutants
UV light intensity
Photocatalytic degeneration and regeneration.
Titania Research at LSU
Laboratory evaluation of concrete pavement treated with TiO2:
Methods of applications
Impacts of environmental conditions (relative humidity, pollutants flow rate, solar radiation)
Effectiveness on NOx and SO2 degradation
Design variables (aggregate gradation, TiO2 concentration)
Durability of Photocatalytic layer
Photocatalytic Pervious Concrete Pavement
Titania Research at LSU
Laboratory evaluation of asphalt pavement treated with TiO2:
Methods of applications
Impacts of environmental conditions (relative humidity, pollutants flow rate, solar radiation)
Durability & Effects on mix performance (fracture resistance, thermal cracking, and rutting performance)
Photocatalytic Warm-Mix Asphalt
Effect of TiO2 on HMA and WMA aging
Titania Research at LSU
Field evaluation of asphalt and concrete pavement treated with TiO2:
Hassan and co-workers laid the country’s first air-purifying asphalt and concrete photocatalytic pavements on Dec. 20, 2010
Sample Preparation
Application of Water-Based TiO2 Solution
Curing and sprinkling nano-sized
TiO2 particles 10mm thin
surface mixture
with TiO2
Application Method – HMA & WMA
Spray-Coating Application of TiO2:
A thin nano film is spray-coated on each sample
a mixture of TiO2 anatase nanoparticles with an average size of 6nm suspended in an aqueous liquid at 2% by volume.
Photocatalytic Efficiency
NO Reduction Efficiency
-100
0
100
200
300
400
500
0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 5:00 5:30 6:00 6:30 7:00 7:30 8:00
Con
cen
trati
on
(p
pb
)
duration (h:mm)
NOx NO2 NO
Average Reduction Trial 2 - 242 ppb
% Reduction Trial 2 - 56.4%
Light On Light Off
Results and Analysis
Water vapor can have both negative and positive impacts on the environmental performance of TiO2
Durability Results and Analysis –
WMA &HMA
NOx Removal Efficiency decreased after loading in the LWT.
0
10
20
30
40
50
60
SC-64L1 SC-64L2 SC-64L3 SC-70L1 SC-70L2 SC-70L3N
Ox R
edu
ctio
n E
ffic
ien
cy
Sample ID
Before LWT
After LWT
0.0
5.0
10.0
15.0
20.0
25.0
H64CO H64-7 H70CO H70-7 W64CO W64-7 W70CO W70-7
Ru
t D
ep
th (
mm
)
Mixture ID
HMA WMA
Durability Results and Analysis -
Concrete
Durability: Loaded-Wheel Tester
The measured rut depth for all specimens was minimal (less than 1mm).
Experimental Testing
Abrasion testing: according to ASTM C 944
Test method uses a cutter rotating at 200 rpm under a
constant load of 98 N for 2 minutes to wear the
coating surface.
Durability Results and Analysis -
concrete
A thin coating would be more susceptible to abrasion than the photocatalytic compound applied using the sprinkling method or using the PT product.
Effect of Weathering
LWT slightly improved the NO removal efficiency of the different samples
The weathering action exposed part of the embedded titanium dioxide particles at the surface
Pervious Concrete
Samples are prepared in two layers:
Bottom lift: standard pervious concrete
Upper lift: prepared with photocatalytic specialty cement
Depth of the photocatalytic layer was varied between four levels: 0.5, 1, 2, and 3 in.
Effect of TiO2 depth
The increase in depth resulted in an increase in NOx
removal efficiency
9%
30%
35% 39%
50%
9%
34% 40%
45%
53%
0%
10%
20%
30%
40%
50%
60%
70%
Control 0.5 1 2 3
Rem
oval
Eff
icie
ncy
Depth (inch)
NOx NO
Field Installation
First field installation of TiO2 on pavement in the US (12/2010)
The test area is a pavement site located on LSU campus
Many states (e.g., Virginia, Texas, Vermont, New York, and Missouri) will or are evaluating the technology
The spray coating used was a mixture of TiO2 anatase nanoparticles with an average size of 6nm suspended in an aqueous liquid at 2% by volume
Field Installation
A customized distributor truck was used in the
application of TiO2 water-based solution
Field Monitoring : Direct Method
NO concentration is measured at the pavement
level by placing a perforated pipe at the surface in
the middle of the lane
Field Effectiveness
Indirect Method: Nitrate Analysis
Field measurements were conducted to quantify the amount nitrate deposited on the pavement surface
𝑁𝑂 + 𝑂 𝐻𝑇𝑖𝑂2
𝑁𝑂2 + 𝐻.
𝑁𝑂2 + 𝑂 𝐻𝑇𝑖𝑂2 𝑁𝑂
3 + 𝐻.
Field Effectiveness
There is definite evidence that photocatalytic
degradation of nitrogen oxide is taking place
in the field in the treated section
0
0.1
0.2
0.3
0.4
0.5
1 2 3 4 5 6 7
Avera
ge N
itra
te (
mg/l
)
Day
Treated Section Untreated Section
Cost Analysis
Cost Increase is 4.4%
Costs will decrease significantly once TiO2 is mass produced in the US reducing in both material and delivery costs.
Cost Estimate Cost ($/yd2) 2009 RS Means 10 inch concrete paving surface 42.93
Photocatalytic Coating 1.88
Conclusions
Applying TiO2 as close as possible to the source of pollution can remove a significant portion of NOx pollutants from the atmosphere when placed.
Field measurements show that photocatalytic degradation of nitrogen oxide is taking place in the field in the treated section.
Conclusions
The NO removal efficiency decreased with the increase in humidity level Water inhibits absorption of NO by the photocatalytic
compound
As the flow rate increased, the percent NO removal efficiency decreased As the residence time decreased, it allows less time for
the pollutants to be absorbed by the photocatalytic compound
Additional work is needed..
Evaluate influence of other pollutants (VOCs) and
mixed air pollutants.
Full-scale controlled evaluation in accelerated
facility is needed
Long-term environmental performance and
durability
Assess the potential impacts of photocatalytic TiO2
pavement surface coating on the aquatic
environment
Acknowledgments
This research was sponsored through LTRC, NSF, and
the Gulf Coast Research Center for Evacuation and
Transportation Resiliency
The assistance of the concrete and asphalt
laboratory staff at LTRC is greatly appreciated
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